007 add telemetry

app/controllers/middleware.py

@@ -1,10 +1,55 @@
 """HTTP middleware registration."""
 
-from fastapi import FastAPI
+from uuid import uuid4
+from time import perf_counter
+
+from fastapi import FastAPI, Request
+from starlette.middleware.base import BaseHTTPMiddleware
+from starlette.responses import Response
+from structlog.contextvars import bind_contextvars, clear_contextvars
+
+from app.observability.metrics import get_metrics
+
+
+class RequestCorrelationMiddleware(BaseHTTPMiddleware):
+    """Assign and propagate request correlation identifiers."""
+
+    def __init__(self, app: FastAPI, *, request_id_header: str) -> None:
+        super().__init__(app)
+        self._request_id_header = request_id_header
+
+    async def dispatch(self, request: Request, call_next) -> Response:
+        request_id = str(uuid4())
+        request.state.request_id = request_id
+        bind_contextvars(request_id=request_id)
+
+        started_at = perf_counter()
+        status_code = 500
+        is_error = True
+
+        try:
+            response = await call_next(request)
+            status_code = response.status_code
+            is_error = status_code >= 500
+            response.headers[self._request_id_header] = request_id
+            return response
+        finally:
+            duration_ms = (perf_counter() - started_at) * 1000
+            get_metrics().record_http_request(
+                method=request.method,
+                route=request.url.path,
+                status_code=status_code,
+                duration_ms=duration_ms,
+                is_error=is_error,
+            )
+            clear_contextvars()
 
 
 def install_middleware(app: FastAPI) -> None:
     """Register middleware components for the API."""
 
-    # Middleware stack is introduced in later tasks.
-    _ = app
+    settings = app.state.settings
+    app.add_middleware(
+        RequestCorrelationMiddleware,
+        request_id_header=settings.controller.request_id_header,
+    )